The ubiquitous occurrence of taurine in mammalian tissues and the implication that it or isethionic acid (a metabolite) is involved in the regulation of ion flux in cardiac tissue and the further possiblity that these sulfonic acids may have a function as neurotransmitters in the central nervous system has stimulated renewed interest in both the metabolism and pharmacology of these compounds. This proposal provides an approach to delineate the taurine-isethionic acid pathway in mammalian tissues by characterization of the enzymes which are involved. If the mammalian system is analogous to known microbial systems then a transamination reaction in which sulfoacetaldehyde is formed will be the initial step in the pathway. In order to realize this goal, highly sensitive and specific assay systems will be designed. Furthermore, it has been reported that in heart tissue, catecholamines and cardiac glycosides affect the rate of conversion of taurine to isethionic acid and thus the mechanism(s) of action for these compounds will be investigated. The only function for these sulfonic acids that has been well documented is the conjugation of taurine with bile acids and the involvement of isethionic acid in preventing the loss of potassium ions from cardiac tissue thereby alleviating drug-induced (epinephrine and cardiac glycosides) arrhythmias. A rapid and extremely sensitive assay procedure for analyzing taurine levels in mammalian tissues based on an enzymatic derivative double isotope method will be designed and then a definitive study will be undertaken to measure rodent tissue levels of taurine and isethionic acid thereby exploring the relationship between their concentration and anatomical location. Emphasis will be placed on the sulfonic acid levels in cardiac and nervous tissues since present data suggest a role for them in these tissues.